What are the differential diagnoses for a patient presenting with left lower quadrant abdominal pain, fever, and leukocytosis suggestive of diverticulitis?

Differential Diagnoses for Left Lower Quadrant Pain with Fever and Leukocytosis

When a patient presents with left lower quadrant pain, fever, and leukocytosis, the primary diagnosis is acute sigmoid diverticulitis, but you must systematically exclude perforated colon cancer, epiploic appendagitis, inflammatory bowel disease, gynecologic pathology (in women), pyelonephritis, and bowel obstruction. 1, 2

Primary Diagnosis: Acute Diverticulitis

• Acute sigmoid or descending colonic diverticulitis is the most common cause of left lower quadrant pain in adults, particularly those over 50 years old 1, 2
• The classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of diverticulitis cases, making clinical diagnosis unreliable with misdiagnosis rates of 34-68% 1, 2
• CT abdomen and pelvis with IV contrast is mandatory (rated 8/9 by the American College of Radiology) with 98-99% diagnostic accuracy 1, 2

Critical Differential: Perforated Colon Cancer

• Perforated colon cancer can mimic both clinical and radiographic findings of diverticulitis—this is the most dangerous diagnosis to miss 1
• CT findings suggesting cancer rather than diverticulitis include pericolonic lymphadenopathy measuring >1 cm in short axis with or without pericolonic edema 1, 2
• When inflammatory changes and edema in the root of the sigmoid mesentery are present WITHOUT pericolonic lymphadenopathy adjacent to thickened colon wall, diverticulitis is most likely 1
• Colonoscopy is warranted after CT-confirmed diverticulitis only when abscess, perforation, fistula, abnormal lymph nodes, or luminal mass is identified 1, 2

Epiploic Appendagitis

• This is a rare but important mimic of diverticulitis that presents with localized left lower quadrant pain but typically WITHOUT fever or leukocytosis 3, 4
• Patients are characteristically afebrile, and only 12.9% show leukocytosis—this distinguishes it from diverticulitis where 80% have leukocytosis 4
• CT shows a pericolic fatty mass with a hyperattenuated ring in nearly all cases 4
• If your patient has left lower quadrant pain but is afebrile with normal white blood cell count, strongly consider epiploic appendagitis rather than diverticulitis 4

Inflammatory Bowel Disease (IBD)

• Crohn's disease or ulcerative colitis can present with left lower quadrant pain, fever, and leukocytosis 5
• CT findings include bowel wall thickening, but look for skip lesions (Crohn's), involvement of multiple bowel segments, and absence of diverticula 5
• History of chronic diarrhea, bloody stools, or weight loss points toward IBD rather than acute diverticulitis 5

Gynecologic Pathology (Premenopausal Women)

• In premenopausal women, obtain beta-hCG testing before CT and consider pelvic/transvaginal ultrasound as initial imaging if gynecologic pathology is suspected 1, 2
• Differential includes ovarian torsion, ruptured ovarian cyst, tubo-ovarian abscess, and ectopic pregnancy 1, 2
• Cyclical pain pattern suggests gynecologic etiology 6

Pyelonephritis and Nephrolithiasis

• Left-sided pyelonephritis or renal calculi can cause left lower quadrant pain with fever and leukocytosis 2, 5
• CT with IV contrast distinguishes these from diverticulitis by showing perinephric fat stranding, hydronephrosis, or calculi 2
• Urinalysis showing pyuria or hematuria points toward urinary tract pathology 5

Bowel Obstruction

• Large bowel obstruction can present with left lower quadrant pain, though fever and leukocytosis suggest complicated obstruction with ischemia or perforation 1
• Complete inability to pass gas or stool combined with abdominal distension is present in 90% of large bowel obstructions 2
• CT shows dilated bowel loops proximal to the point of obstruction 1

Appendiceal Diverticulitis

• Though typically causing right lower quadrant pain, appendiceal diverticulitis can occasionally present atypically and has higher perforation risk than routine appendicitis 7
• CT may show intramural gas micro-loculations and saccular appendiceal contour with asymmetric periappendiceal fat stranding 7

Imaging Strategy to Differentiate

• Order CT abdomen and pelvis with IV contrast immediately—do not rely on clinical examination alone given the 34-68% misdiagnosis rate 1, 2
• CT identifies alternative diagnoses in approximately 49% of patients with non-localized pain 2
• Look specifically for: pericolonic lymphadenopathy (suggests cancer), pericolic fatty mass with hyperattenuated ring (epiploic appendagitis), skip lesions (IBD), perinephric stranding (pyelonephritis), or dilated bowel loops (obstruction) 1, 4

Common Pitfalls to Avoid

• Do not assume diverticulitis based on history alone—even patients with known diverticulosis can develop alternative pathology including cancer 1, 3
• Do not skip beta-hCG testing in women of reproductive age before ordering CT 2
• Do not order routine colonoscopy after uncomplicated CT-confirmed diverticulitis unless age-appropriate screening is due or concerning CT features are present 1, 2
• In patients who are afebrile without leukocytosis, strongly reconsider the diagnosis of diverticulitis and look for epiploic appendagitis on CT 4